This invention relates generally to cable terminations, and more particularly to a cable terminal assembly for flexible, duel-lead conductor cables of the "kickless" or low reactance level type.
Flexible, dual-lead conductor cables of the "kickless" or low reactance level type are well known in the art and are commonly employed as welding cables for connecting welding heads or guns to transformers providing current for resistance welding operations. Such cables are employed to reduce or eliminate the violent jerks or kicks resulting from the reaction of opposite polarity conductors to one another when high currents are impressed on the cable. Generally, these cables each comprise two leads or groups of multiple strand conductors which are alternately circumferentially disposed and helically wound along the cable length. The ends of the cables are secured to terminals for subsequent connection to the welding heads or transformers. Provisions may be made for fluid coolng of the welding cable assembly.
Although such cables successfully have eliminated or substantially reduced the problem of cable "kick", additional problems stem from the connection of the conductors of the same lead to respective terminal lug halves for subsequent connection to the welding heads and transformers. Substantially all mechanical failures in service occur in this part of the welding cable assembly. This problem is one for which many solutions have been sought as seen in the following U.S. Pat. Nos. 2,308,673; 2,702,311; 2,943,133; 3,127,467; 3,143,593; 3,163,704; 3,456,064; and 3,467,767. It therefore has been long recognized that the manner in which cable conductors are connected to the terminal is of major importance in obtaining substantial service life in view of the severe service requirements imposed on welding cables.
It is common manufacturing practice to join together the cable conductors of each cable lead and secure the same to respective, mutually insulated terminal halves or lugs by soldering, clamping or employing detachable cable conductor connectors. The conductors of the same lead usually are bent and/or twisted to obtain the proper alignment of the same for attachment to the respective terminal halves. Each multiple strand cable conductor consists of a large number of fine wires which are strained by such bending and/or twisting and their susceptibility to work-hardening or embrittlement during use is substantially increased thereby leading to premature fracturing of the wires and early failure of the cable assembly. This condition is aggravated further by the high temperatures generally encountered during welding when the cable is carrying high current.
In addition, strands of opposite polarity cross over each other at the termination creating wear points that can cause electrical short circuits. Moreover, because of this cross-over, the alternately disposed relationship of the conductors of opposite leads is disturbed, particularly at the critical failure area, thus inducing a physical reaction between the conductors in this area thereby further contributing to early deterioration of the cable.
In an early attempt to overcome the above-noted problems in welding cable assemblies, Botterhill disclosed in his U.S. Pat. No. 2,702,311 a cable terminal assembly for six conductor strand "kickless" cables comprising two three-way apertured and longitudinally spaced-apart extensions at the inner or rear ends of the mutually insulated terminal halves of a split cylindrical terminal. The rearwardmost extension of one of the terminal halves is longitudinally spaced from the forwardmost extension of the other terminal half by a neck which is received in an enlarged slot in the forwardmost extension in concentric and interlocking fashion, and the respective apertures of the two extensions are positioned alternately relative to each other when viewed from the rear end of the terminal whereby the apertures of both extensions are aligned respectively with the conductors of the cable. The ends of the conductors are then inserted into and soldered in place in the corresponding apertures of the terminal in order to achieve conductivity through the joint and to secure the cable to the terminal. Although the cable terminal assembly of this type eliminates the before mentioned residual stresses in the cable at the critical failure area and maintains the conductor strands alternately disposed, such cable terminal assembly is subject to several shortcomings. For example, the terminal halves are of complicated structure and therefore expensive to manufacture and difficult mutually to insulate. In addition, the heat generated during the soldering process may embrittle the conductor strand wires contributing to their early fracture and thus early failure of the cable. Moreover, when the conductor strands become broken or burned, repair and/or replacement of the damaged conductors is a difficult procedure and usually must be done at the cable manufacturer's facility resulting in costly repair and freight charges.
In a later attempt to overcome the noted problems, Toto in his U.S. Pat. No. 3,456,064 disclosed a cable termination assembly for a four conductor cable comprising a tubular cable conductor connector adapted to be connected to one of the terminal halves of a split terminal which is so orientated by suitably twisting its cable conductor receiving end such that it is aligned with the helix or lay of two of the conductors of the same cable lead. The remaining two conductors of the other cable lead are either separately secured to the other terminal half by separate connectors having a squared forward end and a diverging rear end which is also orientated with the lay of the respective individual conductors, or jointly secured by a single connector which is formed to include a U-shape channel which straddles the twisted connector. Although such cable termination assembly appears to reduce the residual stresses at the connection between the cable and terminal body, the copper strands are severely distorted by the twisting of the conductor terminal, and furthermore, the assembly proces is difficult and time consuming requiring complex dies for swaging the connectors to the desired shape. Moreover, there is no teaching as to how such a cable terminal assembly could effectively be employed with cables having more than four conductors.